This invention relates to a process for etching semiconductor devices, and more particularly to a process for effectively and efficiently etching multi-layer semiconductor devices while maintaining intact the electrical characteristics of these devices.
It is known in the prior art that the manufacture of multi-layer semiconductor devices typically involves patterned etching using liquid or wet etching materials, or dry etching with halogens or halogen-containing compounds, of certain layers which comprise features these devices. For example, one well known etching material is chlorine which can exist in the etching process as either chlorine gas or HCl, etc. Chlorine etches the semiconductor isotropically, i.e., in both a lateral and vertical direction. This results in an etched feature which has a line width which is smaller than the resist image.
Etching can also be conducted in a gas phase using known techniques such as plasma etching, ion beam etching, and reactive ion etching. The use of gas plasma technology provides substantially anisotropic etching using gaseous ions, typically generated by an RF discharge. In gas plasma etching the requisite portion of the surface to be etched is removed by a chemical reaction between the gaseous ions and the subject surface. In the anisotropic process, etching takes place only or primarily in the vertical direction so that feature widths substantially match the photoresist pattern widths. U.S. Pat. No. 4,734,157 an elemental silicon-containing layer, such as a layer of polysilicon or silicide, is etched anisotropically employing a gas plasma comprising a gaseous chlorofluorocarbon, capable of supplying CFx and chlorine ions, and ammonia. Profile control of a silicon layer is controlled by the use of this etching mode.
A problem which occurs during the gas plasma etching process is profile control which can result in undercutting, i.e., forming negatively sloped sidewalls, of the semiconductor layers below the outer layer of the semiconductor device. For example, if the metal layer is aluminum or an aluminum alloy (particularly those alloys containing copper), a gaseous chlorine or HCl etchant will readily react with the aluminum to form aluminum trichloride and will isotropically etch, and thereby undercut the aluminum layer sidewalls.
Control of this chemical reaction, and in turn control of the profile of a predominantly metal layer in a semiconductor structure, is difficult at best. Various chloro- or fluoro-hydrocarbons which form polymeric additives, such as CCl4, CHCl3, CH3Cl, CHF3, etc., have been used for depositing carbon onto the sidewall to controlling the undercutting problem. However, these deposits can foul the interior of the plasma chamber, are difficult to clean, and are toxic in nature. Silicon-based additives which are combined in the etching mixture, deposit silicon or silicon compounds on the sidewall of the plasma chamber as they are formed. These additives keep the photoresist from reticulating and flowing. BCl3 is also a known halogenated additive.
If oxygen or oxygen-containing compounds are added to silicon-containing plasma, a glass is formed therewith. Although this glass will protect the sidewalls, the free oxygen from the oxygen-containing compounds used to form the glass will also have the undesirable effect of chemically attacking the photoresist.
Therefore, a need exists for a process which prevents, in semiconductors having at least one predominantly metallic layer, the formation of upright metallic sidewalls which form a substantially negative slope during the patterned etching of the metallic layers, and which avoids the use of additives thereby avoiding the plasma chamber fouling problem.